John N. Sherwood: Studies of Energetic Materials

Abstract

Studies on the physicomechanical properties of commonly used energetic materials (EMs) that were pursued by the group led by Professor John Sherwood are reviewed in this paper. The studies ranged from the growth of high quality single crystals and the characterization of their defect and dislocation structures, mechanical testing, through to the study of polymorphism of EM crystals and fundamental aspects of crystallization processes in general. The work performed led to the definition of good growth conditions for all the EMs studied and to the full characterization of the defect structure, slip systems, and hardness properties of cyclotrimethylene trinitramine (RDX) and pentaerythritol tetranitrate (PETN). Partial characterization of the defect structures and hardness properties of cyclotetramethylene tetranitramine (HMX) and 2,4,6-trinitrotoluene (TNT) was also achieved. Additionally, fundamental crystal growth and polymorph information were defined, allowing a deeper understanding of the crystallization and crystal structure of TNT. In addition to the general review, some thoughts were given as to possible future routes for further study that could suitably utilize the complementary nature of established and modern techniques.

Identifying Possible Slip Systems of Molecular Crystals via a Geometry-Based Procedure

“…The most recent experimental study identified two major slip systems in β-HMX to be (001)[100] and (101)[101̅]. It is shown that the preferable slip systems (101)[010] and (101)[101̅] predicted in this work are in general agreement with the above-mentioned experimental reports. − The predicted (011)[100] and (011)[111̅] slip systems have also been identified by atomistic simulations. , Two favorable slip systems (011)[100] and (010)[100] for β-HMX are shown in Figure b. However, our geometric analysis procedure is not able to predict the slip system (001)[100] observed by most experimental studies because (001) has not been identified as a favorable slip plane by the CSD geometric analysis tool.…”

“…Microhardness study on vertical Bridgman technique-grown trans -stilbene single crystals revealed that the most active slip systems are (100)[010], (201̅)[010], and (001)[010], in which (100)[010] is predicted by the present work as the most preferable slip system (Figure f). The dominant operative slip system by microhardness indentation study of monoclinic TNT was estimated to be {001}[010], but further confirmation is required . We show that both (001)[100] (Figure g) and (001)[010] are active slip systems, and more concrete evidence is needed to identify the active slip systems in TNT.…”

“…Pal and Picu evaluated the Peierls–Nabarro critical stress for dislocation motion in a large number of slip systems in β-HMX by atomistic simulations and confirmed that (101)[101̅] is a twinning system and identified low Peierls–Nabarro stress slip systems such as (011)[011̅], (011)[100], (021)[100], and (101)[010]. The most recent experimental study identified two major slip systems in β-HMX to be (001)[100] and (101)[101̅]. It is shown that the preferable slip systems (101)[010] and (101)[101̅] predicted in this work are in general agreement with the above-mentioned experimental reports. − The predicted (011)[100] and (011)[111̅] slip systems have also been identified by atomistic simulations. , Two favorable slip systems (011)[100] and (010)[100] for β-HMX are shown in Figure b.…”

Aspects of Isostructurality and Polymorphism in a Diverse Group of Monosubstituted Acetanilides

“…This paper is concerned with the understanding of the crystalline state of a group of small organic molecules of pharmaceutical significance and adopts the view of the late Olga Kennard that the collective use of data will lead to new knowledge. Recently, the crystal structure assembly of functionalized organic molecules has attracted considerable interest due to its importance in the controlled production of biologically active molecules (pharmaceuticals − ) and other industrially important materials (agrochemicals , ) as well as in the search for solids with utilizable properties (dyes and pigments, , highly energetic materials, , and electronics). Studies involving intermolecular interactions, crystal engineering, and crystal structure prediction are essential to the understanding of the solid state …”

Exposed Facets and Surface Properties of Highly Explosive RDX Studied by the Crystal-Face-Indexing Method and Theoretical Calculations

“…Surface morphology and characteristics of a crystal are fundamentally determined by its facet type and area distribution because functional group distribution, polarity, roughness, and defects on the surface can be predicted by the atomic model of the facets built from the corresponding crystal structure . Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) (cyclotrimethylenetrinitramine) is a kind of elemental energetic material, which has wide applications in mixed explosives due to its high detonation energy, low cost, and good thermal stability. − RDX is also used as additives in solid propellants to enhance the energy of the propellant. − The sensitivity, mechanical properties, and detonation performances of RDX have been found to be significantly affected by its crystal morphology and surface properties. − For example, adhesion measured between the F2314 (fluorinated polymer) binder and the (210), (020), and (002) facets of RDX by the direct tensile experiments were 51, 106, and 152 mJ·m –2 , respectively, demonstrating the anisotropic binding abilities between the F2314 binder and the RDX crystal . Theoretical calculations also reveal that different interfacial microstructures can be formed by different facets with solvent molecules, leading to different crystal habits of RDX. − Due to the importance of facets on the crystal morphology and performances of RDX, accurate analysis of facets is essential in the applications of RDX.…”